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- Dalirian, Maryam, 1978-
(författare)
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On the liquid-phase cloud activation of insoluble and slightly soluble particles
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aerosol-cloud interactions are among the largest sources of uncertainty in understanding climate change and predictions of the future climate. Besides the physical dimensions of aerosol particles, their water-solubility and surface tension are the key properties needed to describe their potential to act as cloud condensation nuclei (CCN). This thesis aims to improve the understanding of the role of atmospherically relevant aerosol mixtures in cloud formation by 1) cloud activation measurements of aerosol particles containing both water-soluble and insoluble components; 2) molecular-level measurements of the surface properties of aqueous solutions for atmospherically relevant organic compounds.In the first part of our study the cloud activation of particles containing ammonium sulfate, sucrose or BSA (bovine serum albumin), and their mixtures with insoluble silica was investigated through laboratory experiments. The CCN activity of the particles was governed by the fraction of soluble material in them. If the soluble fraction could be reliably estimated, the CCN activation of these particles could be successfully predicted with existing theoretical frameworks. Our results showed an uneven distribution of soluble material on the insoluble silica cores in our wet-generated particles. This highlights the need for controlled particle generation and coating techniques.In the second part of this work, the microscopic surface structure of aqueous succinic acid (an atmospherically relevant organic compound) solutions were determined and connected to the macroscopic surface tension of the solution. The molecular data derived from the combination of X-ray Photoelectron Spectroscopy (XPS) experiments and Molecular Dynamics (MD) simulations allowed for derivation of surface enrichment factors for succinic acid in aqueous solutions. These enrichment factors were used for direct estimations of the surface tensions of these mixtures, which showed a good agreement with experimental data. This study thus confirmed the connection between microscopic surface structure and macroscopic surface tension.Despite our effort to investigate the aerosol properties controlling CCN activation and cloud formation, there is still much to learn about cloud activation of complex atmospheric aerosol particles. In this regard, further examining the CCN activation of other insoluble materials like soot or dust, developing controlled coating techniques, investigating the molecular properties of particles consisting organic and inorganic compounds, as well as studying the ice nuclei activity of mixed particles are of particular importance.
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| 2. |
- Werner, Josephina, et al.
(författare)
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Succinic acid in aqueous solution : connecting microscopic surface composition and macroscopic surface tension
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:39, s. 21486-21495
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Tidskriftsartikel (refereegranskat)abstract
- The water vapor interface of aqueous solutions of succinic acid, where pH values and bulk concentrations were varied, has been studied using surface sensitive X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. It was found that succinic acid has a considerably higher propensity to reside in the aqueous surface region than its deprotonated form, which is effectively depleted from the surface due to the two strongly hydrated carboxylate groups. From both XPS experiments and MD simulations a strongly increased concentration of the acid form in the surface region compared to the bulk concentration was found and quantified. Detailed analysis of the surface of succinic acid solutions at different bulk concentrations led to the conclusion that succinic acid saturates the aqueous surface at high bulk concentrations. With the aid of MD simulations the thickness of the surface layer could be estimated, which enabled the quantification of surface concentration of succinic acid as a multiple of the known bulk concentration. The obtained enrichment factors were successfully used to model the surface tension of these binary aqueous solutions using two different models that account for the surface enrichment. This underlines the close correlation of increased concentration at the surface relative to the bulk and reduced surface tension of aqueous solutions of succinic acid. The results of this study shed light on the microscopic origin of surface tension, a macroscopic property. Furthermore, the impact of the results from this study on atmospheric modeling is discussed.
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